Field of the Invention
Conventionally, there have been apparatuses for adjusting the specific volume of intake air of an automobile engine to control the engine speed to a desired value. The prior art apparatuses suffer from the problem that a sudden change in electrical load on a generator, which is driven by the engine, causes a change in torque load on the engine, resulting in a decrease in engine speed due to a time delay of the speed controlling operation.
Japanese Patent Preliminary Publication No. 59-83600 and U.S. Pat. No. 4,459,489 disclose apparatuses in which the output current of the generator slowly increases in response to the sudden increase in electrical load on the generator.
FIG. 4 illustrates the operation of one such prior art apparatus when a feedback control of the engine speed is being performed. A load signal M denotes the presence and absence of an electrical load on the generator. As soon as the generator is applied with an electrical load, the output voltage V of the generator drops and then slowly increases to the value before the load is applied; thus the output current i slowly increases. A feedback correction signal I denotes a feedback correction amount for bringing the difference between an actual speed and a desired speed of the engine, and is used to increase the specific volume of intake air in accordance with the increase in load on the generator such that the engine speed is maintained at the desired value. In this manner, when a large load is applied on the generator while the feedback control is being performed, the engine speed N can be maintained generally at a desirable condition though it undergoes little change.
The dotted lines in FIG. 4 show the responses of the output current i of the generator, the feedback control amount I, and the speed N which results if the output voltage of the generator is maintained constant rather than dropping as depicted by the solid line when the large load is applied. The sudden increase in the output current i as shown in the dotted line causes an increase of torque load on the engine which in turn causes the abrupt drop of the engine speed N. Meanwhile, the feedback correction amount I is applied with some delay time, therefore the engine speed N returns through a damped oscillation to the value before the large electrical load is applied. As mentioned above, in the prior art apparatus, too large a change in engine speed can be prevented when the electrical load is applied while the feedback control of the engine speed is being performed.
However, it should be noted that an automobile engine will encounter the following phenomenon. In FIG. 5, a signal S represents engine conditions, being L when the engine is idle and H when the engine is loaded. During the loaded condition, the feedback control of the engine speed is not carried out; therefore the feedback amount I is zero. At this time, if the electrical load M is applied to the generator, then the output current i of the generator slowly increases responding to the change in load and does not affect the engine speed since the engine output is inherently large at this time. As soon as the engine goes into the idling condition (i.e., S=L), the feedback control of the engine speed is begun but the engine speed N is no longer maintained constant, dropping rapidly as depicted in the solid line since the output current i being drawn from the generator is large enough to impose a heavy load on the engine. The feedback correction amount I slowly increases to cause an increase in the specific volume of intake air of the engine such that the decrease in the engine speed N may be recovered. Due to the delay time in feedback correction, the engine speed N approaches a target value through a damped oscillation.
As mentioned above, in the prior art speed control apparatus, the change in the engine speed N can be retarded when the electrical load is applied to the generator while the feedback control of the engine speed is being carried out, but the engine speed will change greatly if the feedback control of the engine speed is begun while the electrical load is being applied.